Add experimental Codex agent bundle support for lc init

[MaxRonce]

EDIT PR closed, should be tested on my fork first, missclicked

Adds experimental Codex support as an agent backend for lc init, while preserving the existing Claude Code behavior

New flow test :

The new install flow is:

lc init --agent codex my-analysis
cd my-analysis
codex

Changes

• Adds generic agent bundle discovery with get_agent_bundle_source_dir(agent).
• Keeps get_plugin_source_dir() as a Claude-compatible wrapper.
• Adds lc init --agent {claude,codex,none,both}.
• Keeps claude as the default behavior.
• Installs Codex projects with AGENTS.md and .agents/skills/.
• Ensures Codex mode does not install .claude/ or CLAUDE.md.
• Adds a minimal Codex bundle: astra, lc-cli, lc-new, lc-from-code.
• Includes codex/lightcone in wheel and sdist packaging.
• Documents the new Codex install flow and experimental status.

Tests / Checks

Ran:

uv run pytest
uv run mypy src/
uv run ruff check src/ tests/
uv build

Also smoke-tested:

uv run lc init /tmp/... --no-git --no-venv
uv run lc init --agent codex /tmp/... --no-git --no-venv

Verified default lc init still creates CLAUDE.md and .claude/; lc init --agent codex creates AGENTS.md and .agents/skills/; wheel and sdist include codex/lightcone.

Misc

• Still experimental, will test it in my fork
• Some claude feature not implemented + codex bundle smaller for the moment
• lc-from-paper is not ported to Codex
• Claude-specific hooks, permissions, and subagent behavior are not replicated for Codex atm

[MaxRonce]

Ran some experiments to support codex instead of claude.
The PR was supposed to be from my fork/feature https://github.com/MaxRonce/lightcone-cli/tree/main to the my fork/main https://github.com/MaxRonce/lightcone-cli/tree/main